1. Field of the Invention
The present invention relates to a coating composition forming a coating film on the surface of articles, and in particular to a coating composition suitable to coating the surface of articles which are exposed to water such as a heat exchanger to be used in an air-conditioner.
2. Discussion of the Background
To the surface of kinds of articles used indoors/outdoors, various contamination such as powder dust, dust, greasy fume, tobacco tar, etc. stick. Therefore, kinds of methods for suppressing them have been proposed. For example, in order to suppress sticking of contamination of powder dust, a method for coating antistatic agent on the surface of articles to prevent electrostatically sticking of powder dust is known. Further, in order to suppress sticking of lipophilic contamination such as greasy fume, a method for coating oil-repellent fluorine resin on the surface of articles to prevent sticking of lipophilic contamination or to facilitate removing contamination is known.
However, in these methods, there is a problem that a coating film formed on the surface of articles by coating may be separated, property to prevent sticking of contamination may be degraded, and it is impossible to maintain the antifouling property for a long term. Therefore, another method for forming a surface in which a hydrophilic part and a hydrophobic part are mutually independently exposed in a minute region to maintain the antifouling property for a long term is attempted.
As one of examples, there is a method for coating the surface of articles with resin coating film having microphase-separated structure composed of hydrophilic part and hydrophobic part by applying coating composition including polymers having functional group, hydrophilic microparticles, metal alkoxide, and solvent on the surface of articles (refer to Patent Document 1, for example).
Further, for coating on the surface of a heat exchanger used for an air-conditioner, in order to prevent attachment of waterdrop of dewed water, antifouling coating composition, in which photocatalystic oxide and water-repellent fluorine resin are microscopically dispersed in a surface layer, exposed to contact outdoor air, and a contact angle θ with water of the surface of the layer is equal to or greater than 90 degrees, is proposed (refer to Patent Documents 2 and 3, for example).
Further, similar to the above, for coating on the surface of the heat exchanger, antifouling coating composition, in which a surface layer is composed of silica layer including microscopically dispersed photocatalystic oxide and water-repellent fluorine resin, and the amount of photocatalystic oxide is 10 to 80% by weight in the surface layer, and the amount of water-repellent fluorine resin is 20 to 60% by weight in the surface layer, is proposed (refer to Patent Document 4, for example).
Further, although not from the viewpoint of antifouling, in order to improve hydrophilia of the surface of heat exchanger, a method, in which the surface of heat exchanger is coated by triethanolamine solution, sodium carbonate solution, or ammonia water solution to make a contact angle θ with condensate water (dewed water) equal to or less than 10 degrees, is proposed (refer to Patent Document 5, for example).